Photoemission with the STM

An STM tip has been used to detect photoelectrons emitted from alkali metal -coated aluminium and silicon surfaces whilst within tunnelling range. I-V spectra clearly show a pair of sharp thresholds which are simply related to the tip workfunction, the sample workfunction, and the incident photon ene rgy. The voltages at which these thresholds occur yield a direct, absolute measurement of the surface workfunction. The photoemitted electrons can be detected independently of other laser-induced excitations of the surface, a nd maps of the photocurrent show features on the nanometer length scale whi ch are obviously related to the structure of the surface. Both the spectral and spatial resolution of this technique represent significant advances on previous forms of photoemission or workfunction microscopy. (C) 2000 Elsev ier Science B.V. All rights reserved.